Method and apparatus for video coding using planar intra prediction mode for intra sub-partition coding mode

ABSTRACT

Aspects of the disclosure provide methods, apparatuses, and non-transitory computer-readable storage mediums for video encoding/decoding. Prediction information for a current block in a current picture is determined. The prediction information indicates that the current block is to be encoded in (1) an intra sub-partition (ISP) mode and (2) one of a planar intra prediction mode or a DC intra prediction mode. The current block is partitioned into a plurality of sub-partitions based on the ISP mode. Each sub-partition is associated with at least one different reference sample. Residual information for each sub-partition is generated based on the at least one different reference sample associated with the respective sub-partition. The current block is encoded based on the determined prediction information and the generated residual information of the plurality of sub-partitions.

INCORPORATION BY REFERENCE

This present application is a continuation of U.S. patent applicationSer. No. 16/838,503, “METHOD AND APPARATUS FOR VIDEO CODING USING PLANARINTRA PREDICTION MODE FOR INTRA SUB-PARTITION CODING MODE,” filed onApr. 2, 2020, which claims the benefit of priority to U.S. ProvisionalApplication No. 62/834,901, “IMPROVED PLANAR INTRA PREDICTION MODE FORINTRA SUB-PARTITIONS CODING MODE,” filed on Apr. 16, 2019. Thedisclosures of the prior applications are incorporated by referenceherein in their entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate) of, for example, 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or maybe predicted itself.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 93 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 1B shows a schematic (105) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs of aneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described herein is atechnique henceforth referred to as “spatial merge.”

Referring to FIG. 1C, a current block (111) can include samples thathave been found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (112 through 116, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes processing circuitry.

According to aspects of the disclosure, there is provided a method forvideo decoding in a decoder. In the method, prediction information for acurrent block in a current picture that is a part of a coded videosequence is decoded. The prediction information indicates an intrasub-partition (ISP) mode for the current block. The current block ispartitioned into a plurality of sub-partitions based on the ISP mode.Each of the plurality of sub-partitions is associated with at least onedifferent reference sample that is in (1) a row above the current blockor (2) a column left to the current block. Each of the plurality ofsub-partitions is reconstructed based on the at least one differentreference sample associated with the respective sub-partition. Thecurrent block is reconstructed based on the reconstructedsub-partitions.

In an embodiment, the at least one different reference sample for eachof the plurality of sub-partitions includes reference samples adjacentto the respective sub-partition.

In an embodiment, a sub-partition in the plurality of sub-partitions isreconstructed based on another sub-partition in the plurality ofsub-partitions that is reconstructed.

According to aspects of the disclosure, the prediction informationindicates a planar intra prediction mode for the current block, theplurality of sub-partitions is associated with at least one sharedreference sample, and each of the plurality of sub-partitions isreconstructed based on the at least one different reference sampleassociated with the respective sub-partition and the at least one sharedreference sample.

In an embodiment, the at least one different reference sample associatedwith the respective sub-partition includes a reference sample that isadjacent to (1) a top right corner of the respective sub-partition in acase that the current block is partitioned in the vertical mode or (2) abottom left corner of the respective sub-partition in a case that thecurrent block is partitioned in the horizontal mode.

In an embodiment, the at least one shared reference sample includes areference sample that is adjacent to (1) a bottom left corner of thecurrent block in a case that the current block is partitioned in thevertical mode or (2) a top right corner of the current block in a casethat the current block is partitioned in the horizontal mode.

According to aspects of the disclosure, the prediction informationindicates a DC intra prediction mode for the current block, and each ofthe plurality of sub-partitions is reconstructed based on a respectiveDC value calculated according to the at least one different referencesample associated with the respective sub-partition.

In an embodiment, the current block is partitioned in the vertical mode,and the at least one different reference sample associated with asub-partition in the plurality of sub-partitions that is not adjacent tothe left side of the current block is in the row above the currentblock.

In an embodiment, the current block is partitioned in the horizontalmode, and the at least one different reference sample associated with asub-partition in the plurality of sub-partitions that is not adjacent tothe top side of the current block is in the column left to the currentblock.

Aspects of the disclosure provide an apparatus configured to perform anyone or a combination of the methods for video decoding. In anembodiment, the apparatus includes processing circuitry that decodesprediction information for a current block in a current picture that isa part of a coded video sequence. The prediction information indicatesan intra sub-partition (ISP) mode for the current block. The ISP modeindicates that the current block is to be partitioned in one of avertical mode and a horizontal mode. The processing circuitry partitionsthe current block into a plurality of sub-partitions based on the ISPmode. Each of the plurality of sub-partitions is associated with atleast one different reference sample that is in (1) a row above thecurrent block or (2) a column left to the current block. The processingcircuitry reconstructs each of the plurality of sub-partitions based onthe at least one different reference sample associated with therespective sub-partition. The processing circuitry reconstructs thecurrent block based on the reconstructed sub-partitions.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform any one or acombination of the methods for video decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A shows a schematic illustration of an exemplary subset of intraprediction modes;

FIG. 1B shows an illustration of exemplary intra prediction directions;

FIG. 1C shows a schematic illustration of a current block and itssurrounding spatial merge candidates in one example;

FIG. 2 shows a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment;

FIG. 3 shows a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment;

FIG. 4 shows a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment;

FIG. 5 shows a schematic illustration of a simplified block diagram ofan encoder in accordance with an embodiment;

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment;

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment;

FIGS. 8A and 8B show an example of a block partition by using aquad-tree plus binary tree (QTBT) partitioning structure and thecorresponding QTBT structure;

FIG. 9A shows an example of −vertical center-side TT partitioning;

FIG. 9B shows an example of horizontal center-side TT partitioning;

FIGS. 10A and 10B show exemplary intra prediction directions andcorresponding intra prediction angles in some examples;

FIGS. 11A and 11B show an exemplary planar intra prediction;

FIG. 12A shows an exemplary horizontal ISP mode and an exemplaryvertical ISP mode of a coding block that is coded in ISP mode accordingto an embodiment of the disclosure;

FIG. 12B show an exemplary horizontal ISP mode and an exemplary verticalISP mode of another coding block that is coded in ISP mode according toan embodiment of the disclosure;

FIGS. 13A and 13B show an exemplary coding block that is coded in avertical ISP mode according to embodiments of the disclosure;

FIGS. 13C and 13D show another exemplary coding block that is coded in ahorizontal ISP mode according to embodiments of the disclosure;

FIG. 14A shows an exemplary coding block that is coded in a vertical ISPmode and DC mode according to an embodiment of the disclosure;

FIG. 14B shows another exemplary coding block that is coded in ahorizontal ISP mode and DC mode according to an embodiment of thedisclosure;

FIG. 15 shows a flow chart outlining an exemplary process in accordancewith an embodiment of the disclosure; and

FIG. 16 shows a schematic illustration of a computer system inaccordance with an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

Video Encoder and Decoder

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick, and the like.

A streaming system may include a capture subsystem (313) that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4 . The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values that canbe input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation that the intra prediction unit (452) has generated to theoutput sample information as provided by the scaler/inverse transformunit (451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector allowed reference area,and so forth. The controller (550) can be configured to have othersuitable functions that pertain to the video encoder (503) optimized fora certain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4 . Brieflyreferring also to FIG. 4 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415) andthe parser (420) may not be fully implemented in the local decoder(533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously coded picture fromthe video sequence that were designated as “reference pictures.” In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quad-tree split into one ormultiple CUs. For example, a CTU of 64×64 pixels can be split into oneCU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUs of 16×16 pixels.In an example, each CU is analyzed to determine a prediction type forthe CU, such as an inter prediction type or an intra prediction type.The CU is split into one or more prediction units (PUs) depending on thetemporal and/or spatial predictability. Generally, each PU includes aluma prediction block (PB), and two chroma PBs. In an embodiment, aprediction operation in coding (encoding/decoding) is performed in theunit of a prediction block. Using a luma prediction block as an exampleof a prediction block, the prediction block includes a matrix of values(e.g., luma values) for pixels, such as 8×8 pixels, 16×16 pixels, 8×16pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6 .

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7 .

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (603), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

Block Partitioning Structure Using QTBT

In HEVC, a CTU is split into CUs by using a quad-tree (QT) structuredenoted as a coding tree to adapt to various local characteristics. Thedecision on whether to code a picture area using inter-picture(temporal) or intra-picture (spatial) prediction is made at the CUlevel. Each CU can be further split into one, two or four PUs accordingto a PU splitting type. Inside one PU, the same prediction process isapplied and the relevant information is transmitted to a decoder on a PUbasis. After obtaining a residual block by applying the predictionprocess based on the PU splitting type, a CU can be partitioned intotransform units (TUs) according to another QT structure like the codingtree for the CU.

One key feature of the HEVC structure is that it has multiple partitionconceptions including CU, PU, and TU. The quad-tree plus binary tree(QTBT) structure removes the concepts of multiple partition types, i.e.,it removes the separation of the CU, PU and TU concepts, and supportsmore flexibility for CU partition shapes.

In the QTBT structure, a CU can have either a square or rectangularshape. As shown in FIGS. 8A and 8B, a CTU is first partitioned by a QTstructure. The QT leaf nodes are further partitioned by a binary tree(BT) structure. There are two splitting types, symmetric horizontalsplitting and symmetric vertical splitting, in the BT splitting. The BTleaf nodes are CUs, and segmentation between two CUs is used forprediction and transform processing without any further partitioning.Accordingly, CU, PU and TU can have the same block size in the QTBTstructure.

In some related examples, a CU sometimes can include CBs of differentcolor components, e.g. one CU can contain one luma CB and two chroma CBsin the case of P and B slices with the 4:2:0 chroma formats.Alternatively, a CU can include CBs of a single component, e.g., one CUcan contain only one luma CB or just two chroma CBs in the case of Islices.

The following parameters are defined for the QTBT partitioning scheme:

-   -   CTU size: the root node size of a QT, for example the same        concept as in HEVC    -   MinQTSize: the minimum allowed QT leaf node size    -   MaxBTSize: the maximum allowed BT root node size    -   MaxBTDepth: the maximum allowed BT depth    -   MinBTSize: the minimum allowed BT leaf node size

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 luma samples with two corresponding 64×64 blocks of chromasamples, the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64,the MinBTSize (for both width and height) is set as 4×4, and theMaxBTDepth is set as 4. The QT partitioning is applied to the CTU firstto generate QT leaf nodes. The QT leaf nodes may have a size from 16×16(i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If the leaf QTnode is 128×128, it will not be further split by the BT since the sizeexceeds the MaxBTSize (i.e., 64×64). Otherwise, the leaf QT node couldbe further partitioned by the BT tree. Therefore, the QT leaf node isalso the root node for the BT and it has the BT depth as 0. When the BTdepth reaches MaxBTDepth (i.e., 4), no further splitting is considered.When the BT node has width equal to MinBTSize (i.e., 4), no furtherhorizontal splitting is considered. Similarly, when the BT node has aheight equal to MinBTSize, no further vertical splitting is considered.The leaf nodes of the BT are further processed by prediction andtransform processing without any further partitioning. In some cases,the maximum CTU size is 256×256 luma samples.

In addition, the QTBT scheme supports the flexibility for the luma andchroma to have a separate QTBT structure. Currently, for P and B slices,the luma and chroma CTBs in one CTU share the same QTBT structure.However, for I slices, the luma CTB is partitioned into CUs by a QTBTstructure and the chroma CTBs are partitioned into chroma CUs by anotherQTBT structure. Accordingly, a CU in an I slice includes a coding blockof the luma component or coding blocks of two chroma components, and aCU in a P or B slice includes coding blocks of all three colorcomponents.

In HEVC, inter prediction for small blocks is restricted to reduce thememory access of motion compensation, such that bi-prediction is notsupported for 4×8 and 8×4 blocks, and inter prediction is not supportedfor 4×4 blocks. In the QTBT structure, these restrictions are removed.

FIG. 8A illustrates an example of a block partition (8100) by using aQTBT partitioning structure (8200) and FIG. 8B illustrates thecorresponding QTBT structure (8200). The solid lines indicate QT splitsand the dotted lines indicate binary tree BT splits. In each non-leaf BTsplit node, a flag is signaled to indicate a splitting type (i.e., asymmetric horizontal split or a symmetric vertical split). For example,in the FIG. 8B example, “0” indicates a symmetric horizontal split and“1” indicates a symmetric vertical split. For a QT split, however, asplit type flag is not indicated or signaled because the QT split splitsa non-leaf node both horizontally and vertically to produce four smallerblocks with an equal size.

Referring to FIG. 8B, in the QTBT structure (8200), a root node (8201)is first partitioned by a QT structure into QT nodes (8211-8214).Accordingly, as shown in FIG. 8A, a coding tree block (8101) ispartitioned into four equal size blocks (8111-8114) by the solid lines.

Referring back to FIG. 8B, the QT nodes (8211) and (8212) are furthersplit by two BT splits, respectively. As mentioned above, a BT splitincludes two splitting types, i.e., a symmetric horizontal split and asymmetric vertical split. The non-leaf QT node (8211) is indicated as“1” and thus can be split into two nodes (8221) and (8222) by using asymmetric vertical split. The non-leaf QT node (8212) is indicated as“0” and thus can be split into two nodes (8223) and (8224) by using asymmetric horizontal split. The non-leaf QT node (8213) is further splitinto four nodes (8225-8228) by another QTBT structure. The node (8214)is not further split and thus a leaf node. Accordingly, as shown in FIG.8A, the block (8111) is vertically partitioned into two equal sizeblocks (8121) and (8122), the block (8112) is horizontally partitionedinto two equal size blocks, the block (8113) is partitioned into fourequal size blocks, and the block (8114) is not further partitioned.

Referring back to FIG. 8B, in deeper levels, some of the nodes(8221-8228) are further split while the others are not. For example, thenon-leaf BT node (8221) is further split into two leaf nodes (8231) and(8232) by a symmetric vertical split while the leaf node (8222) is notfurther split. Accordingly, as shown in FIG. 8A, the block (8121) ispartitioned into two equal size blocks (8131) and (8132) while the block(8122) is not further partitioned.

After splitting of the QTBT structure (8200) is completed, leaf nodesthat are not further split are CUs that are used for prediction andtransform processing. Thus, a CU, a PU that is associated with the CU,and a TU that is associated with the CU can have a same block size inthe QTBT structure. In addition, in the QTBT structure, a CU can includeCBs in different color components. For example, in a 4:2:0 format, oneCU can include one luma CB and two chroma CBs in a P or B slice.However, in some other embodiments, a CU may include CBs in a singlecomponent. For example, in an I slice, one CU may include one luma CB ortwo chroma CBs. That is to say, the QTBT structure supports an abilityfor luma and chroma to have different partitioning structures.

Block Partitioning Structure Using Triple-Trees

In addition to the QTBT structure described above, another splittingstructure called the multi-type-tree (MTT) structure is also proposed inVVC and can be more flexible than the QTBT structure. In an MTTstructure, other than quad-tree and binary-tree, horizontal and verticalcenter-side triple-trees (TTs) are introduced, as shown in FIG. 9A andFIG. 9B. A triple-tree partitioning can also be referred to as a ternarytree partitioning.

FIG. 9A shows an example of vertical center-side TT partitioning. Forexample, a block (910) is vertically split into three sub-blocks(911-913) where the sub-block (912) is located in the middle of theblock (910).

FIG. 9B shows an example of horizontal center-side TT partitioning. Forexample, a block (920) is horizontally split into three sub-blocks(921-923) where the sub-block (922) is located in the middle of theblock (920).

Similar to a BT split, in a TT split, a flag is signaled to indicate asplitting type (i.e., a symmetric horizontal split or a symmetricvertical split). In an example, “0” indicates a symmetric horizontalsplit and “1” indicates a symmetric vertical split.

A MTT structure, including quad-tree, binary-tree, and ternary-treesplitting types, is referred to as a QTBTTT structure. Similar to a QTBTstructure, a QTBTTT structure also supports luma and chroma havingdifferent structures. For example, in an I slice, a QTBTTT structureused to partition a luma CTB can be different from a QTBTTT structureused to partition a chroma CTB. Accordingly, when a separated treestructure is enabled, a CU includes one luma CB or two chroma CBs.However, in a P or B slice, a luma CTB can share the same QTBTTTstructure with a chroma CTB in one CTU. Accordingly, when the separatedtree structure is disabled, a CU includes all three CBs, i.e., one lumaCB and two chroma CBs.

Intra Prediction in VVC

FIG. 10A shows an illustration of exemplary intra prediction directionsand corresponding intra prediction modes in some examples (e.g., VVC).In FIG. 10A, there are a total of 95 intra prediction modes (modes−14˜80), among which mode 0 is a planar mode (referred to asINTRA_PLANAR), mode 1 is a DC mode (referred to as INTRA_DC), and othermodes (modes −14˜−1 and modes 2˜80) are angular (or directional) modes(also referred to as INTRA_ANGULAR). Among the angular (or directional)modes, mode 18 (referred to as INTRA_ANGULAR18) is a horizontal mode,mode 50 (referred to as INTRA_ANGULAR50) is a vertical mode, and mode 2(referred to as INTRA_ANGULAR2) is a diagonal mode that points to abottom left direction, mode 34 (referred to as INTRA_ANGULAR34) is adiagonal mode that points to a top-left direction, and mode 66 (referredto as INTRA_ANGULAR66) is a diagonal mode that points to a top rightdirection. Modes −14˜−1 and Modes 67˜80 are referred to as wide-angleintra prediction (WAIP) modes.

In addition, a vertical-like intra prediction direction is defined as anintra prediction direction which is associated with a prediction anglethat falls into a range of (V−Thr, V+Thr), where V is the predictionangle of the vertical mode and Thr is a given threshold. Similarly, ahorizontal-like intra prediction direction is defined as an intraprediction direction which is associated with a prediction angle thatfalls into (H−Thr, H+Thr), where H is the prediction angle of thehorizontal mode and Thr is the given threshold.

FIG. 10B shows exemplary angular intra prediction modes and theircorresponding intra prediction angles. preModeIntra denotes the intraprediction modes and intraPredAngle denotes the intra prediction anglesof the intra prediction modes. The precision of the intra predictionangles is 1/32. For one intra prediction mode, if its associated angleis X, then its actual angle is X/32. For example, for mode 66, itsassociated angle is 32 and its actual angle is 32/32.

Planar Intra Prediction

FIGS. 11A and 11B show an exemplary planar intra prediction. The planarintra prediction is generated with an average of two linearinterpolations (i.e., horizontal and vertical interpolations). Forexample, a right column and a bottom row of a current block aregenerated by replicating a top right pixel and a bottom left pixeladjacent to the current block, respectively. In FIGS. 11A and 11B,pixels (1110) and (1120) are adjacent to a top right corner and a bottomleft corner of a current block (1100). The top right pixel (1110) isreplicated to a pixel (1130) located in the right column of the currentblock (1110). The bottom left pixel (1120) is replicated to a pixel 1140located in the bottom row of the current block (1110). Accordingly, apixel (1150) inside the current block (1100) can be reconstructed basedon the pixels (1130) and (1140). It is noted that the pixel (1150) andthe pixel (1130) are in the same row of the current block (1100). Inaddition, the pixel (1150) and the pixel (1140) are in the same columnof the current block (1100).

Intra Sub-Partition (ISP) Coding Mode

A luma coding block that is coded in intra sub-partition (ISP) codingmode can be vertically (in a vertical ISP mode) or horizontally (in ahorizontal ISP mode) partitioned into a plurality of sub-partitions(e.g., 2 or 4) depending on a block size of the block, as shown inTable. 1. For example, all sub-partitions fulfill a condition of havingat least 16 samples. For chroma components, the ISP mode may not beapplied.

TABLE 1 Number of sub-partitions depending on the block size Block SizeNumber of Sub-Partitions 4 × 4 Not divided 4 × 8 and 8 × 4 2 All othercases 4

In some embodiments, the ISP mode can only be tested with intra modesthat are part of a most probable mode (MPM) list. Accordingly, if acoding block is coded in ISP mode, then an MPM flag of the MPM list canbe inferred to be, for example, one or true. In some cases, the MPM listcan be modified to exclude DC mode and to prioritize horizontal intraprediction modes for the horizontal ISP mode and vertical intraprediction modes for the vertical ISP mode.

In addition, each sub-partition of the coding block can be regarded as asub-TU, since transform and reconstruction can be performed individuallyfor each sub-partition.

FIG. 12A shows an exemplary horizontal ISP mode and an exemplaryvertical ISP mode of a coding block (1200) that is coded in ISP modeaccording to an embodiment of the disclosure. In the FIG. 12A example, ablock size of the coding block (1200) is W1×H1, which for example iseither 4×8 or 8×4 samples. Accordingly, the coding block (1200) ispartitioned into 2 sub-partitions. As shown in FIG. 12A, the codingblock (1200) can be horizontally partitioned into two sub-partitions(1211-1212) with each having a size of W1×H1/2 samples for thehorizontal ISP mode, or vertically partitioned into two sub-partitions(1221-1222) with each having a size of W1/2×H1 samples for the verticalISP mode.

FIG. 12B show an exemplary horizontal ISP mode and an exemplary verticalISP mode of another coding block (1250) that is coded in ISP modeaccording to an embodiment of the disclosure. In the FIG. 12B example, ablock size of the coding block (1250) is W2×H2, which is for exampleabove 4×8 or 8×4 samples. Accordingly, the coding block (1250) ispartitioned into 4 sub-partitions. As shown in FIG. 12B, the codingblock (1250) can be horizontally partitioned into four sub-partitions(1261-1264) with each having a size of W2×H2/4 samples, or verticallypartitioned into four sub-partitions (1271-1274) with each having a sizeof W2/4×H2 samples.

For each of these sub-partitions, a residual signal can be generatedthrough entropy decoding of coefficients sent by an encoder and thenthrough inverse quantizing and inverse transforming of the coefficients.Then, for one of the sub-partitions, which can be referred to as acurrent sub-partition, a prediction signal can be generated byperforming intra prediction on the current sub-partition. Finally,reconstructed samples of the current sub-partition can be obtained byadding the residual signal to the prediction signal.

The reconstructed samples of the current sub-partition can be used topredict another sub-partition, for example that is next to the currentsub-partition. This process can be repeated to other sub-partitionssince all sub-partitions can share the same intra prediction mode.

In some related examples, for a planar intra prediction, when a codingblock is horizontally partitioned, top right neighboring sample(s)(e.g., the top right pixel 1110 in FIG. 11A) of one or moresub-partitions can be unavailable. For example, when the coding block ishorizontally partitioned into four sub-partitions as shown in FIG. 12B,top right neighboring samples of second, third, and fourthsub-partitions (1272-1274) are marked unavailable. Similarly, when thecoding block is vertically partitioned, bottom left neighboringsample(s) (e.g., the bottom left pixel 1120 in FIG. 11A) of one or moresub-partitions can be unavailable. For example, when the coding block isvertically partitioned into four sub-partitions as shown in FIG. 12B,bottom left neighboring samples of second, third, and fourthsub-partitions (1262-1264) are marked unavailable.

Improved Intra Prediction for ISP Mode

Aspects of the present disclosure provide methods, apparatuses, andnon-transitory computer-readable storage mediums for improving intraprediction of a CU that is coded in an ISP mode. For example,embodiments of the present disclosure can address cases in which one ormore neighboring samples of a sub-partition are unavailable. The methodsmay be used separately or combined in any order. Further, the term blockmay be interpreted as a PB, a coding block, or a CU. An adjacentreference line is a reference line closest to the current block andassociated with reference line index 0.

According to aspects of the disclosure, for a coding block that is codedin ISP mode, when the ISP mode is enabled, the current block can bepartitioned into a plurality of sub-partitions based on the ISP mode,and each of the plurality of sub-partitions is associated with at leastone different reference sample. The at least one different referencesample can be in either a row above the current block or a column leftto the current block.

In an embodiment, the at least one different reference sample for eachof the plurality of sub-partitions includes reference samples adjacentto the respective sub-partition.

According to aspects of the disclosure, for a coding block that is codedin ISP mode, when the ISP mode is enabled and planar mode is used forthe coding block, the plurality of sub-partitions of the coding block isassociated with at least one shared reference sample, in addition to theat least one different reference sample associated with eachsub-partition. Accordingly, each of the plurality of sub-partitions canbe reconstructed based on the at least one different reference sampleassociated with the respective sub-partition and the at least one sharedreference sample.

FIGS. 13A and 13B show an exemplary coding block (1300) that is coded ina vertical ISP mode according to embodiments of the disclosure. The ISPmode of the coding block (1300) is a vertical mode. Accordingly, thecoding block (1300) is vertically partitioned into a plurality ofsub-partitions (1301-1304).

In an embodiment, reconstruction of a sub-partition (e.g., thesub-partition 1301) can be performed earlier than reconstruction of oneor more subsequent sub-partitions (e.g., the sub-partition 1302), andreconstructed samples of the sub-partition (e.g., the sub-partition1301) can be used for one or more subsequent sub-partitions (e.g., thesub-partition 1302). At least one neighboring reference sample(s) (e.g.,left and/or bottom left neighboring reference sample) of thesub-partition can be used for the remaining sub-partitions, anddifferent sub-partitions can use at least one different neighboringreference sample (e.g., above and/or top right neighboring referencesample(s)) for planar prediction when the coding block (1300) is codedin planar mode.

In an embodiment, one or more sub-partitions inside the coding block(1300) can be predicted by using reconstructed samples adjacent to thecoding block (1300). The one or more sub-partitions include all of thesub-partitions (1301-1304) in one example. All the sub-partitions(1301-1304) can share the same at least one left and/or bottom leftneighboring reference sample, but use at least one different aboveand/or top right neighboring reference sample for planar prediction whenthe coding block (1300) is coded in planar mode.

In some embodiments, the at least one different reference sampleassociated with each of the plurality of sub-partitions can be in a rowabove the coding block (1300). As shown in FIG. 13A, above neighboringreference samples (1311-1314) can include the reference samples for thesub-partitions (1301-1304), respectively. It is noted that the aboveneighboring reference samples (1311-1314) are in the same row above thecoding block (1300). In addition, it is noted that in other embodiments,one reference sample, instead of a plurality of reference samples, foreach of the sub-partitions can be used to perform the intra prediction.

In some embodiments, the at least one different reference sampleassociated with each of the plurality of sub-partitions includes areference sample that is adjacent to a top right corner or a top side ofthe respective sub-partition. As shown in FIG. 13B, top rightneighboring reference samples (1321-1324) can be associated with thesub-partitions (1301-1304), respectively. Each of the top rightneighboring reference samples (1321-1324) is adjacent to a top rightcorner of the respective sub-partition. For example, the top rightneighboring reference sample (1322) is adjacent to a top right corner ofthe sub-partition (1302).

In some embodiments, at least one reference sample can be shared amongthe sub-partitions (1301-1304) for planar prediction when the codingblock (1300) is coded in planar mode. In an embodiment, as shown in FIG.13A, all the sub-partitions (1301-1304) can share the same leftneighboring reference samples (1315) that is left to the coding block(1300), but use different above neighboring reference samples(1311-1314) for planar prediction when the coding block (1300) is codedin planar mode. In another embodiment, as shown in FIG. 13B, all thesub-partitions (1301-1304) can share the same bottom left referencesample (1325) adjacent to a bottom left corner, or a bottom side, of thecoding block (1300), but use different top right neighboring referencesamples (1321-1324) for planar prediction when the coding block (1300)is coded in planar mode.

In an embodiment, a sub-partition in the plurality of sub-partitions(1301-1304) is reconstructed based on another sub-partition in theplurality of sub-partitions (1301-1304) that is reconstructed. Forexample, when a block size of the coding block (1300) is 8×N (N>4), athird sub-partition (1303) and/or fourth sub-partition (1304) can usereconstructed samples of a second sub-partition (1302) for intraprediction, the top right neighboring reference samples used for planarprediction for each sub-partition can be shown in FIG. 13B. Further, insome embodiments, all the sub-partitions (1301-1304) can share the samebottom left reference sample (1325) adjacent to the bottom left corneror the bottom side of the coding block (1300).

FIGS. 13C and 13D show another exemplary coding block (1340) that iscoded in a horizontal ISP mode according to embodiments of thedisclosure. The ISP mode of the coding block (1340) is a horizontalmode. Accordingly, the coding block (1340) is horizontally partitionedinto a plurality of sub-partitions (1351-1354).

In an embodiment, reconstruction of a sub-partition (e.g., thesub-partition 1351) can be performed earlier than reconstruction of oneor more subsequent sub-partitions (e.g., the sub-partition 1352), andreconstructed samples of the sub-partition (e.g., the sub-partition1351) can be used for one or more subsequent sub-partitions (e.g., thesub-partition 1352). At least one neighboring reference sample (e.g.,above and/or top right neighboring reference sample(s)) of thesub-partition can be used for the remaining sub-partitions, anddifferent sub-partitions can use at least one different neighboringreference sample (e.g., left and/or bottom left neighboring referencesample(s)) for planar prediction when the coding block (1340) is codedin planar mode.

In an embodiment, one or more sub-partitions inside the coding block(1340) can be predicted by using reconstructed samples adjacent to thecoding block (1340). The one or more sub-partitions include all of thesub-partitions (1351-1354) in one example. All the sub-partitions(1351-1354) can share the same at least one above and/or top rightneighboring reference samples, but use at least one different leftand/or bottom left neighboring reference samples for planar predictionwhen the coding block (1340) is coded in planar mode.

In some embodiments, the at least one different reference sampleassociated with each of the plurality of sub-partitions can be in acolumn left to the coding block (1340). As shown in FIG. 13C, leftneighboring reference samples (1361-1364) can include the referencesamples for the sub-partitions (1351-1354), respectively. It is notedthat the left neighboring reference samples (1361-1364) are in the samecolumn left to the coding block (1340). In addition, it is noted that inother embodiments, one reference sample, instead of a plurality ofreference samples, for each of the sub-partitions can be used to performthe intra prediction.

In some embodiments, the at least one different reference sampleassociated with each of the plurality of sub-partitions includes areference sample that is adjacent to a bottom left corner or a left sideof the respective sub-partition. As shown in FIG. 13D, bottom leftneighboring reference samples (1371-1374) can be associated with thesub-partitions (1351-1354), respectively. Each of the bottom leftneighboring reference samples (1371-1374) is adjacent to a bottom leftcorner of the respective sub-partition. For example, the bottom leftreference sample (1372) is adjacent to a bottom left corner of thesub-partition (1352).

In some embodiments, at least one reference sample can be shared amongthe sub-partitions (1351-1354) for planar prediction when the codingblock (1340) is coded in planar mode. In an embodiment, as shown in FIG.13C, all the sub-partitions (1351-1354) can share the same aboveneighboring reference samples (1365) that is above the coding block(1340), but use different left neighboring reference samples (1361-1364)for planar prediction when the coding block (1340) is coded in planarmode. In another embodiment, as shown in FIG. 13D, all thesub-partitions (1351-1354) can share the same top right reference sample(1375) adjacent to a top right corner, or a top side, of the codingblock (1340), but use different bottom left neighboring referencesamples (1371-1374) for planar prediction when the coding block (1340)is coded in planar mode.

In an embodiment, a sub-partition in the plurality of sub-partitions(1351-1354) is reconstructed based on another sub-partition in theplurality of sub-partitions (1351-1354) that is reconstructed. Forexample, when a block size of the coding block (1340) is N×8 (N>4), athird sub-partition (1353) and/or fourth sub-partition (1354) can usereconstructed samples of a second sub-partition (1352) for intraprediction, the bottom left neighboring reference samples used forplanar prediction for each sub-partition can be shown in FIG. 13D.Further, in some embodiments, all the sub-partitions (1351-1354) canshare the same bottom left reference sample (1375) adjacent to the topright corner or the top side of the coding block (1340).

According to aspects of the disclosure, for a coding block that is codedin ISP mode, when the ISP mode is enabled and DC mode is used for thecoding block, each of the plurality of sub-partitions can bereconstructed based on a respective DC value calculated according to (orby using) the at least one different reference sample associated withthe respective sub-partition.

FIG. 14A shows an exemplary coding block (1400) that is coded in avertical ISP mode and DC mode according to an embodiment of thedisclosure. In the FIG. 14A example, the ISP mode of the coding block(1400) is a vertical mode. Accordingly, the coding block (1400) isvertically partitioned into a plurality of sub-partitions (1401-1404).

In an embodiment, for a first sub-partition (1401), which is adjacent toa left side of the coding block (1400), left neighboring referencesamples (1415) or above neighboring reference samples (1411) can be usedto calculate the corresponding DC value used in DC mode. The leftneighboring reference samples (1415) are adjacent to the left side ofthe coding block (1400). The above neighboring reference samples (1411)are in a row above the coding block (1400). For remaining sub-partitions(1402-1404), only above neighboring reference samples (1412-1414) can beused to calculate the corresponding DC values used in DC mode. Forexample, only the above neighboring reference samples (1413) can be usedto calculate the DC value of a third sub-partition (1403). It is notedthat the above neighboring reference samples (1411-1414) are in the samerow above the coding block (1400). In addition, it is noted that inother embodiments, one reference sample, instead of a plurality ofreference samples, for each of the sub-partitions can be used tocalculate the corresponding DC value used in DC mode.

In one embodiment, when a size of the coding block (1400) is 4×N or 8×N(N>4), only the left neighboring samples (1415) can be used to calculatethe DC value of a first sub-partition (1401), and only the aboveneighboring samples (1412-1414) can be used to calculate the DC valuesof the remaining sub-partitions (1402-1404).

FIG. 14B shows another exemplary coding block (1440) that is coded in ahorizontal ISP mode and DC mode according to an embodiment of thedisclosure. In the FIG. 14B example, the ISP mode of the coding block(1440) is a horizontal mode. Accordingly, the coding block (1440) ishorizontally partitioned into a plurality of sub-partitions (1451-1454).

In an embodiment, for a first sub-partition (1451), which is adjacent toa top side of the coding block (1440), left neighboring referencesamples (1461) or above neighboring reference samples (1465) can be usedto calculate the corresponding DC value used in DC mode. The aboveneighboring reference samples (1465) are adjacent to the top side of thecoding block (1440). The left neighboring reference samples (1461) arein a column left to the coding block (1440). For remainingsub-partitions (1452-1454), only left neighboring reference samples(1462-1464) can be used to calculate the corresponding DC values used inDC mode. For example, only the left neighboring samples (1463) can beused to calculate the DC value of a third sub-partition (1453). It isnoted that the left neighboring reference samples (1461-1464) are in thesame column left to the coding block (1440). In addition, it is notedthat in other embodiments, one reference sample, instead of a pluralityof reference samples, for each of the sub-partitions can be used tocalculate the corresponding DC value.

In one embodiment, when a size of the coding block (1440) is N×4 or N×8(N>4), only the above neighboring samples (1465) can be used tocalculate the DC value of a first sub-partition (1451), and only theleft neighboring samples (1462-1464) can be used to calculate the DCvalues of the remaining sub-partitions (1452-1454).

Flow Chart

FIG. 15 shows a flow chart outlining an exemplary process (1500)according to an embodiment of the disclosure. In various embodiments,the process (1500) is executed by processing circuitry, such as theprocessing circuitry in the terminal devices (210), (220), (230) and(240), the processing circuitry that performs functions of the videoencoder (303), the processing circuitry that performs functions of thevideo decoder (310), the processing circuitry that performs functions ofthe video decoder (410), the processing circuitry that performsfunctions of the intra prediction module (452), the processing circuitrythat performs functions of the video encoder (503), the processingcircuitry that performs functions of the predictor (535), the processingcircuitry that performs functions of the intra encoder (622), theprocessing circuitry that performs functions of the intra decoder (772),and the like. In some embodiments, the process (1500) is implemented insoftware instructions, thus when the processing circuitry executes thesoftware instructions, the processing circuitry performs the process(1500).

The process (1500) may generally start at step (S1510), where theprocess (1500) decodes prediction information for a current block in acurrent picture that is a part of a coded video sequence. The predictioninformation indicates an intra sub-partition (ISP) mode for the currentblock. The ISP mode indicates that the current block is to bepartitioned in one of a vertical mode and a horizontal mode. Then theprocess (1500) proceeds to step (S1520).

At step (S1520), the process (1500) partitions the current block into aplurality of sub-partitions based on the ISP mode. Each of the pluralityof sub-partitions is associated with at least one different referencesample that is in (1) a row above the current block or (2) a column leftto the current block. Then the process (1500) proceeds to step (S1530).

At step (S1530), the process (1500) reconstructs each of the pluralityof sub-partitions based on the at least one different reference sampleassociated with the respective sub-partition. Then the process (1500)proceeds to step (S1540).

At step (S1540), the process (1500) reconstructs the current block basedon the reconstructed sub-partitions.

After reconstructing the current block, the process (1500) terminates.

In an embodiment, the at least one different reference sample for eachof the plurality of sub-partitions includes reference samples adjacentto the respective sub-partition.

In an embodiment, the process (1500) reconstructs a sub-partition in theplurality of sub-partitions based on another sub-partition in theplurality of sub-partitions that is reconstructed.

According to aspects of the disclosure, the prediction informationindicates a planar intra prediction mode for the current block, theplurality of sub-partitions is associated with at least one sharedreference sample, and the process (1500) reconstructs each of theplurality of sub-partitions based on the at least one differentreference sample associated with the respective sub-partition and the atleast one shared reference sample.

In an embodiment, the at least one different reference sample associatedwith the respective sub-partition includes a reference sample that isadjacent to (1) a top right corner of the respective sub-partition in acase that the current block is partitioned in the vertical mode or (2) abottom left corner of the respective sub-partition in a case that thecurrent block is partitioned in the horizontal mode.

In an embodiment, the at least one shared reference sample includes areference sample that is adjacent to (1) a bottom left corner of thecurrent block in a case that the current block is partitioned in thevertical mode or (2) a top right corner of the current block in a casethat the current block is partitioned in the horizontal mode.

According to aspects of the disclosure, the prediction informationindicates a DC intra prediction mode for the current block, and theprocess (1500) reconstructs each of the plurality of sub-partitionsbased on a respective DC value calculated according to the at least onedifferent reference sample associated with the respective sub-partition.

In an embodiment, the current block is partitioned in the vertical mode,and the at least one different reference sample associated with asub-partition in the plurality of sub-partitions that is not adjacent tothe left side of the current block is in the row above the currentblock.

In an embodiment, the current block is partitioned in the horizontalmode, and the at least one different reference sample associated with asub-partition in the plurality of sub-partitions that is not adjacent tothe top side of the current block is in the column left to the currentblock.

Computer System

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 16 shows a computersystem (1600) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 16 for computer system (1600) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1600).

Computer system (1600) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1601), mouse (1602), trackpad (1603), touchscreen (1610), data-glove (not shown), joystick (1605), microphone(1606), scanner (1607), camera (1608).

Computer system (1600) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1610), data-glove (not shown), or joystick (1605), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1609), headphones(not depicted)), visual output devices (such as screens (1610) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted). These visual output devices (such as screens(1610)) can be connected to a system bus (1648) through a graphicsadapter (1650).

Computer system (1600) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1620) with CD/DVD or the like media (1621), thumb-drive (1622),removable hard drive or solid state drive (1623), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1600) can also include a network interface (1654) toone or more communication networks (1655). The one or more communicationnetworks (1655) can for example be wireless, wireline, optical. The oneor more communication networks (1655) can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of the one or more communication networks (1655) includelocal area networks such as Ethernet, wireless LANs, cellular networksto include GSM, 3G, 4G, 5G, LTE and the like, TV wireline or wirelesswide area digital networks to include cable TV, satellite TV, andterrestrial broadcast TV, vehicular and industrial to include CANBus,and so forth. Certain networks commonly require external networkinterface adapters that attached to certain general purpose data portsor peripheral buses (1649) (such as, for example USB ports of thecomputer system (1600)); others are commonly integrated into the core ofthe computer system (1600) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1600) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1640) of thecomputer system (1600).

The core (1640) can include one or more Central Processing Units (CPU)(1641), Graphics Processing Units (GPU) (1642), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1643), hardware accelerators for certain tasks (1644), and so forth.These devices, along with Read-only memory (ROM) (1645), Random-accessmemory (1646), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1647), may be connectedthrough the system bus (1648). In some computer systems, the system bus(1648) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1648),or through a peripheral bus (1649). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1641), GPUs (1642), FPGAs (1643), and accelerators (1644) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1645) or RAM (1646). Transitional data can be also be stored in RAM(1646), whereas permanent data can be stored for example, in theinternal mass storage (1647). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1641), GPU (1642), massstorage (1647), ROM (1645), RAM (1646), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1600), and specifically the core (1640) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1640) that are of non-transitorynature, such as core-internal mass storage (1647) or ROM (1645). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1640). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1640) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1646) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1644)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

APPENDIX A: ACRONYMS

-   -   AMVP: Advanced Motion Vector Prediction    -   ASIC: Application-Specific Integrated Circuit    -   ATMVP: Alternative/Advanced Temporal Motion Vector Prediction    -   BDOF: Bi-directional Optical Flow    -   BIO: Bi-directional Optical Flow    -   BMS: Benchmark Set    -   BV: Block Vector    -   CANBus: Controller Area Network Bus    -   CB: Coding Block    -   CBF: Coded Block Flag    -   CCLM: Cross-Component Linear Mode/Model    -   CD: Compact Disc    -   CPR: Current Picture Referencing    -   CPUs: Central Processing Units    -   CRT: Cathode Ray Tube    -   CTBs: Coding Tree Blocks    -   CTUs: Coding Tree Units    -   CU: Coding Unit    -   DPB: Decoder Picture Buffer    -   DVD: Digital Video Disc    -   FPGA: Field Programmable Gate Areas    -   GOPs: Groups of Pictures    -   GPUs: Graphics Processing Units    -   GSM: Global System for Mobile communications    -   HDR: High Dynamic Range    -   HEVC: High Efficiency Video Coding    -   HRD: Hypothetical Reference Decoder    -   IBC: Intra Block Copy    -   IC: Integrated Circuit    -   ISP: Intra Sub-Partitions    -   JEM: Joint Exploration Model    -   JVET: Joint Video Exploration Team    -   LAN: Local Area Network    -   LCD: Liquid-Crystal Display    -   LTE: Long-Term Evolution    -   MPM: Most Probable Mode    -   MTS: Multiple Transform Selection    -   MV: Motion Vector    -   OLED: Organic Light-Emitting Diode    -   PBs: Prediction Blocks    -   PCI: Peripheral Component Interconnect    -   PDPC: Position Dependent Prediction Combination    -   PLD: Programmable Logic Device    -   PU: Prediction Unit    -   RAM: Random Access Memory    -   ROM: Read-Only Memory    -   SBT: Sub-block Transform    -   SCC: Screen Content Coding    -   SDR: Standard Dynamic Range    -   SEI: Supplementary Enhancement Information    -   SNR: Signal Noise Ratio    -   SSD: Solid-state Drive    -   TUs: Transform Units    -   USB: Universal Serial Bus    -   VPDU: Visual Process Data Unit    -   VUI: Video Usability Information    -   VVC: Versatile Video Coding    -   WAIP: Wide-Angle Intra Prediction

What is claimed is:
 1. A method for video encoding in an encoder,comprising: determining prediction information for a current block in acurrent picture, the prediction information indicating that the currentblock is encoded in (1) an intra sub-partition (ISP) mode and (2) one ofa planar intra prediction mode or a DC intra prediction mode;partitioning the current block into a plurality of sub-partitions basedon the ISP mode, each of the plurality of sub-partitions beingassociated with at least one different reference sample; generatingresidual information for each of the plurality of sub-partitions basedon the at least one different reference sample associated with therespective sub-partition; and encoding the current block based on (1)the one of the planar intra prediction mode or the DC intra predictionmode and (2) the generated residual information of the plurality ofsub-partitions.
 2. The method of claim 1, wherein the predictioninformation indicates that the current block is encoded in the planarintra prediction mode, the plurality of sub-partitions is associatedwith at least one shared reference sample that is shared among theplurality of sub-partitions, and the generating the residual informationfor each of the plurality of sub-partitions includes generating theresidual information for each of the plurality of sub-partitions basedon the at least one different reference sample associated with therespective sub-partition and the at least one shared reference sample.3. The method of claim 2, wherein the at least one different referencesample associated with the respective sub-partition includes a referencesample that is adjacent to (1) a top right corner of the respectivesub-partition based on the current block being partitioned in a verticalmode or (2) a bottom left corner of the respective sub-partition basedon the current block being partitioned in a horizontal mode.
 4. Themethod of claim 2, wherein the at least one shared reference sampleincludes a reference sample that is adjacent to (1) a bottom left cornerof the current block based on the current block being partitioned in avertical mode or (2) a top right corner of the current block based onthe current block being partitioned in a horizontal mode.
 5. The methodof claim 1, wherein the prediction information indicates that thecurrent block is encoded in the DC intra prediction mode, and thegenerating the residual information for each of the plurality ofsub-partitions includes generating the residual information for each ofthe plurality of sub-partitions based on a respective DC valuecalculated according to the at least one different reference sampleassociated with the respective sub-partition.
 6. The method of claim 5,wherein the current block is partitioned in a vertical mode, and the atleast one different reference sample associated with a sub-partition inthe plurality of sub-partitions is in a row above the current blockbased on the sub-partition not being adjacent to a left side of thecurrent block.
 7. The method of claim 5, wherein the current block ispartitioned in a horizontal mode, and the at least one differentreference sample associated with a sub-partition in the plurality ofsub-partitions is in a column left to the current block based on thesub-partition not being adjacent to a top side of the current block. 8.The method of claim 1, wherein the generating the residual informationfor each of the plurality of sub-partitions comprises: generating theresidual information for a first sub-partition in the plurality ofsub-partitions based on a second sub-partition in the plurality ofsub-partitions, the residual information of the second sub-partitionbeing generated before the residual information of the firstsub-partition.
 9. The method of claim 1, wherein the at least onedifferent reference sample for each of the plurality of sub-partitionsincludes reference samples adjacent to the respective sub-partition. 10.An apparatus, comprising: processing circuitry configured to: determineprediction information for a current block in a current picture, theprediction information indicating that the current block is encoded in(1) an intra sub-partition (ISP) mode and (2) one of a planar intraprediction mode or a DC intra prediction mode; partition the currentblock into a plurality of sub-partitions based on the ISP mode, each ofthe plurality of sub-partitions being associated with at least onedifferent reference sample; generate residual information for each ofthe plurality of sub-partitions based on the at least one differentreference sample associated with the respective sub-partition; andencode the current block based on (1) the determined predictioninformation one of the planar intra prediction mode or the DC intraprediction mode and (2) the generated residual information of theplurality of sub-partitions.
 11. The apparatus of claim 10, wherein theprediction information indicates that the current block is encoded inthe planar intra prediction mode, the plurality of sub-partitions isassociated with at least one shared reference sample that is sharedamong the plurality of sub-partitions, and the processing circuitry isfurther configured to generate the residual information for each of theplurality of sub-partitions based on the at least one differentreference sample associated with the respective sub-partition and the atleast one shared reference sample.
 12. The apparatus of claim 11,wherein the at least one different reference sample associated with therespective sub-partition includes a reference sample that is adjacent to(1) a top right corner of the respective sub-partition based on thecurrent block being partitioned in a vertical mode or (2) a bottom leftcorner of the respective sub-partition based on the current block beingpartitioned in a horizontal mode.
 13. The apparatus of claim 11, whereinthe at least one shared reference sample includes a reference samplethat is adjacent to (1) a bottom left corner of the current block basedon the current block being partitioned in a vertical mode or (2) a topright corner of the current block based on the current block beingpartitioned in a horizontal mode.
 14. The apparatus of claim 10, whereinthe prediction information indicates that the current block is encodedin the DC intra prediction mode, and the processing circuitry is furtherconfigured to generate the residual information for each of theplurality of sub-partitions based on a respective DC value calculatedaccording to the at least one different reference sample associated withthe respective sub-partition.
 15. The apparatus of claim 14, wherein thecurrent block is partitioned in a vertical mode, and the at least onedifferent reference sample associated with a sub-partition in theplurality of sub-partitions is in a row above the current block based onthe sub-partition not being adjacent to a left side of the currentblock.
 16. The apparatus of claim 14, wherein the current block ispartitioned in a horizontal mode, and the at least one differentreference sample associated with a sub-partition in the plurality ofsub-partitions is in a column left to the current block based on thesub-partition not being adjacent to a top side of the current block. 17.The apparatus of claim 10, wherein the processing circuitry is furtherconfigured to: generate the residual information for a firstsub-partition in the plurality of sub-partitions based on a secondsub-partition in the plurality of sub-partitions, the residualinformation of the second sub-partition being generated before theresidual information of the first sub-partition.
 18. The apparatus ofclaim 10, wherein the at least one different reference sample for eachof the plurality of sub-partitions includes reference samples adjacentto the respective sub-partition.
 19. A non-transitory computer-readablestorage medium storing a program executable by at least one processor toperform: determining prediction information for a current block in acurrent picture, the prediction information indicating that the currentblock is encoded in (1) an intra sub-partition (ISP) mode and (2) one ofa planar intra prediction mode or a DC intra prediction mode;partitioning the current block into a plurality of sub-partitions basedon the ISP mode, each of the plurality of sub-partitions beingassociated with at least one different reference sample; generatingresidual information for each of the plurality of sub-partitions basedon the at least one different reference sample associated with therespective sub-partition; and encoding the current block based on (1)the one of the planar intra prediction mode or the DC intra predictionmode and (2) the generated residual information of the plurality ofsub-partitions.
 20. The non-transitory computer-readable storage mediumof claim 19, wherein the at least one different reference sample foreach of the plurality of sub-partitions includes reference samplesadjacent to the respective sub-partition.